FR3098390A1 - Method for estimating the quality of a heart rate signal - Google Patents

Abstract

Method for estimating the quality of a heart rate signal The present description relates to a method for estimating, by means of an electronic processing device (104), the quality of a heart rate signal (OUT) supplied by a heartbeat sensor (102) during an acquisition phase of duration W, said signal (OUT) comprising a sequence of N samples IBIi each having a value representative of a duration between two successive heartbeats detected by the sensor (102), with N an integer greater than or equal to 2 and i an integer ranging from 1 to N, the method comprising a step of calculating, by means of the electronic processing device (104), a deficiency indicator L representative the difference between the duration W of the acquisition phase and the sum of the values of the samples IBIi of the signal (OUT). Figure for the abstract: Fig. 1

Description

Method for estimating the quality of a heart rate signal

The present description relates generally to the field of systems using heartbeat sensors, and more particularly aims at a method for estimating the quality of the heartbeat signals provided by such sensors.

The heart rate of a subject is a physiological parameter used in many applications, for example applications for controlling stress, applications for controlling and/or preventing certain chronic diseases, or even applications for controlling physical activity of the subject.

In some applications, the subject is required to wear a heart rate sensor continuously for long periods, for example throughout the day and/or night, in ambulatory conditions. Many sensors suitable for these applications are now commercially available.

For certain applications, the quality of the signals supplied by the existing sensors is however not always sufficient. This is particularly the case for applications exploiting the short-term variability of the heart rate, for example stress control applications. In such applications, a few missed beats can be enough to significantly distort the analyses.

One embodiment provides a method for estimating, by means of an electronic processing device, the quality of a heartbeat signal supplied by a heartbeat sensor during an acquisition phase of duration W, said signal comprising a sequence of N samples IBI _i each having a value representative of a duration between two successive heartbeats detected by the sensor, with N being an integer greater than or equal to 2 and i being an integer ranging from 1 to N, the method comprising a step of calculating, by means of the electronic processing device, a deficiency indicator L representative of the difference between the duration W of the acquisition phase and the sum of the values of the samples IBI _i of the signal.

According to an embodiment of the present invention, the deficiency indicator L is representative of a percentage of heart beats missed by the sensor during the acquisition phase.

According to one embodiment of the present invention, the deficiency indicator L is defined by the following formula:

According to an embodiment of the present invention, in which the duration W of the acquisition phase is between 20 and 120 seconds.

According to an embodiment of the present invention, the method further comprises a step of comparing the deficiency indicator L with a predefined threshold TH and a step of deciding, on the basis of the result of the comparison, to take into account whether or not the heart rate signal is taken into account.

According to an embodiment of the present invention, during the decision step, the heart rate signal is taken into account only if the deficiency indicator L is lower than the threshold TH.

According to an embodiment of the present invention, the threshold TH is defined as follows:
where τ is a tolerance margin between 0 and 100 defining a maximum tolerated percentage of heart beats missed by the sensor during the acquisition phase.

According to an embodiment of the present invention, the margin τ is between 0 and 20.

Another embodiment provides a system comprising a heart rate sensor and an electronic processing device, the electronic processing device being configured to implement a method for estimating the quality of a heart rate signal provided by the sensor as defined above.

These characteristics and their advantages, as well as others, will be explained in detail in the following description of particular embodiments made on a non-limiting basis in relation to the attached figures, among which:

FIG. 1 schematically represents, in the form of blocks, an example of a system comprising a heart rhythm sensor and an electronic processing device suitable for implementing a method for estimating the quality of a rhythm signal cardiac according to one embodiment;

FIG. 2 is a diagram representing, by way of illustration, an example of a heart rhythm signal; And

FIG. 3 schematically represents, in the form of blocks, an example of a method for estimating the quality of a cardiac rhythm signal according to one embodiment.

The same elements have been designated by the same references in the different figures. In particular, the structural and/or functional elements common to the various embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed. In particular, the production of a heart rate sensor suitable for supplying the heart rate signals processed by the quality estimation method of the present application has not been detailed, the embodiments described being compatible with all or most of the known heart rate sensors, or the realization of such a sensor being within the reach of those skilled in the art from the indications of the present description. In addition, the production of an electronic processing device suitable for implementing the method described below for estimating the quality of a heart rate signal has not been detailed, the production of such a device being within the reach of those skilled in the art from the indications of the present description. In addition, the applications capable of exploiting the heart rate signals analyzed by the method of the present application have not been detailed, the embodiments described being compatible with all or most of the applications that can take advantage of the update. provision of an indicator representative of the quality of a heart rate signal supplied by a heart rate sensor.

Unless otherwise specified, when reference is made to two elements connected together, it means directly connected without intermediate elements other than conductors, and when reference is made to two elements connected or coupled together, it means that these two elements can be connected or be linked or coupled through one or more other elements.

Unless specified otherwise, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably within 5%.

FIG. 1 schematically represents, in the form of blocks, an example of a system 100 comprising a heart rate sensor 102 (HR) and an electronic processing device 104 (PROC) configured to implement a method of estimating the quality of a heart rate signal provided by the sensor 102.

The sensor 102 can be an electrocardiograph-type sensor, measuring the electrical activity of the heart by means of electrodes placed in contact with the surface of the subject's skin. As a variant, the sensor 102 can be a sensor of the photoplethysmograph type, measuring the variations of a light signal, for example an infrared signal, on the path of which is placed a blood vessel of the subject (for example at the level of a user's wrist in the case of a bracelet-type sensor). More generally, the embodiments described apply to any type of sensor suitable for measuring a signal representative of the subject's heartbeat.

Considered here more particularly is a sensor providing an output signal OUT in the form of a series of samples each having a value representative of a period between two successive heartbeats detected by the sensor. One can then speak of an instantaneous heart rate signal insofar as each sample is representative of the current inter-beat interval and therefore of the current (instantaneous) heart rate of the subject.

In the example of FIG. 1, the OUT signal is transmitted to an application electronic device 106 (APP) configured to implement a method exploiting the OUT signal, for example a stress control method, a control method and/or or prevention of certain chronic diseases, or even a method of controlling the physical activity of the subject. The connection between the sensor 102 and the device 106 is for example a wired connection.

To generate signal OUT, sensor 102 includes an internal processing circuit, not detailed in the figure. The internal processing circuit generates the signal OUT from a raw analog signal supplied by an acquisition element (not detailed) of the sensor. In practice, depending on the type of sensor used and depending on the conditions of use of the sensor, for example in the event of imperfect positioning of the sensor, certain portions of the analog signal supplied by the acquisition element of the sensor may be too noisy to achieve reliable heartbeat detection. These portions can be identified by the internal processing device of the sensor and are then not taken into account to generate the signal OUT. In addition, certain calculated inter-beat interval values may be deemed aberrant by the sensor's internal processing device, for example if they do not satisfy a predetermined relevance criterion, and are then not transmitted in the output signal OUT of the sensor. Thus, certain heartbeats of the subject are not taken into account for the generation of the signal OUT. In other words, the signal OUT supplied by the sensor 102 is a signal freed or cleaned of any aberrant values. The method implemented by the sensor 102 to generate, from the raw signal, an output signal OUT freed from outliers, will not be detailed, the embodiments described being compatible with all or most of the known cleaning methods. of a raw signal provided by a heart rate sensor.

Depending on the type of application implemented by the device 106, the missing beats can significantly distort the results obtained. In particular, beat deficiencies are particularly problematic for applications exploiting short-term heart rate variability, for example stress control applications.

For this reason, in the system of FIG. 1, the output signal OUT of the sensor 102 is also transmitted to the device 104 which implements a method for estimating the quality of the signal OUT. More particularly, the device 104 calculates an indicator L of the quality of the signal OUT. The indicator L is transmitted to the application device 106 which, on the basis of this indicator, determines whether or not the signal OUT can be exploited by the application. The connection between the sensor 102 and the processing device 104 is for example a wired connection. The connection between the processing device 104 and the application device 106 can also be a wired connection.

The processing device 104 can comprise a microprocessor, or any other processing circuit suitable for implementing the method for calculating the indicator L described below. By way of example, the application device 106 and the processing circuit 104 comprise common elements, for example the same microprocessor.

Figure 2 is a diagram showing, by way of illustration, an example of a heart rate signal. More particularly, the diagram of FIG. 2 represents the evolution, as a function of time t (on the abscissa), of the inter-beat interval IBI (on the ordinate) of the subject.

In FIG. 2, times t ₀ , t ₁ , t ₂ , t ₃ , ... t _N-1 , t _N , t _N+1 have been represented on the abscissa axis, corresponding respectively to times d occurrences of successive heartbeats of the subject. For each of the instants t _i , with i being an integer ranging from 1 to N+1, a point 201 has been represented in FIG. 2 having the instant t _i for the abscissa, and for the ordinate a value IBI _i = t _i -t _{i -1} corresponding to the time interval elapsed between the heart beats of the instants t _{i -1} and t _i .

The output signal OUT of the sensor 102 is for example subsequently made up of the values IBI ₁ , IBI ₂ , IBI ₃ , ..., IBI _N-1 , IBI _N , IBI _N+1 .

FIG. 3 schematically represents, in the form of blocks, an example of a method for estimating the quality of the heart rate signal OUT supplied by the sensor 102, implemented by the processing device 104.

The method of FIG. 3 comprises a step 301 of acquiring signal OUT during an acquisition phase T _acq of duration W, ranging from a time t _start to a time t _end . The duration W of the acquisition phase T _acq is for example between 20 and 120 seconds. However, the embodiments described are not limited to this particular case.

The signal OUT acquired during the acquisition phase T _acq consists of N successive samples IBI ₁ , ..., IBI _N , each representative of a duration between two successive heartbeats of the subject.

When all the heartbeats of the subject are effectively taken into account within the sensor 102 to generate the signal OUT, the sum of the values of the N samples IBI ₁ , ..., IBI _N acquired during the acquisition phase T _acq is close to the duration W of the acquisition phase T _acq . More particularly, considering that the instant t _start at the start of the acquisition phase T _acq can be between two successive heartbeats of the subject, between beats t ₀ and t ₁ in the example shown, and that the the instant t _end of the end of the acquisition phase T _acq can be between two successive heartbeats of the subject, between beats t _N and t _N+1 in the example represented, the following relationship is respected:

If, on the other hand, certain inter-beat intervals of the patient have not been taken into account by the sensor 102 and have therefore not been transmitted in the signal OUT, the sum of the values of the samples IBI ₁ , ..., IBI _N acquired during the acquisition phase T _acq can be substantially less than the duration W of the acquisition phase T _acq .

According to one aspect of the embodiments described, provision is made, during a step 302 subsequent to step 301, to calculate an indicator L representative of the difference between the duration W of the acquisition phase and the sum of the values of the signal samples. This indicator, also called deficiency indicator, is representative of the proportion of inter-beat periods not taken into account by the sensor 102, and is used as an indicator of the quality of the output signal OUT of the sensor 102.

The indicator L is for example defined as follows:

The indicator L is thus representative of the percentage of beats not taken into account in the acquisition window T _acq .

Another way of expressing the indicator L is to consider a theoretical number N _th of samples which should have been acquired during the acquisition phase T _acq , defined as follows: where μ denotes the mean of the values of the samples IBI ₁ , ... IBI _N , i.e.:

We then have:

In FIG. 3, a step 303 has also been represented, subsequent to step 302, for deciding, on the basis of the indicator L, whether or not to take into account the signal OUT acquired during the acquisition phase T _acq . The decision step 303 can be implemented by the application device 106 itself, or by the processing device 104. In the latter case, only a binary value representing the result of the decision can be transmitted to the application device 106 .

The decision step consists for example of comparing the indicator L with a predefined threshold TH, and of taking into account the signal OUT acquired during the acquisition phase T _acq only if the indicator L is lower than the threshold TH.

The threshold TH is for example defined as follows: where τ is a tolerance margin between 0 and 100, for example between 0 and 20, defining the maximum tolerated percentage of missed beats during the acquisition phase T _acq .

By way of example, the acquisition time window T _acq of duration W is a sliding window, the method of FIG. 3 being repeated each time a new sample of signal OUT is supplied by sensor 102. This allows to detect and take into account all the portions of the signal OUT of duration W meeting the quality criterion defined in step 303.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, the embodiments described are not limited to the examples of numerical parameters described above.

Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art based on the functional indications given above.

Claims (9)

Method for estimating, by means of an electronic processing device (104), the quality of a heart rate signal (OUT) supplied by a heart rate sensor (102) during an acquisition phase ( T _acq ) of duration W, said signal (OUT) comprising a sequence of N samples IBI _i each having a value representative of a duration between two successive heartbeats detected by the sensor (102), with N integer greater than or equal to 2 and i an integer ranging from 1 to N, the method comprising a step (302) of calculating, by means of the electronic processing device (104), a deficiency indicator L representative of the difference between the duration W of the phase d acquisition (T _acq ) and the sum of the values of the samples IBI _i of the signal (OUT). Method according to claim 1, in which the deficiency indicator L is representative of a percentage of heartbeats missed by the sensor (102) during the acquisition phase (Tacq). Process according to claim 1 or 2, in which the deficiency indicator L is defined by the following formula:
Method according to any one of Claims 1 to 3, in which the duration W of the acquisition phase (T _acq ) is between 20 and 120 seconds. Method according to any one of Claims 1 to 4, further comprising a step of comparing the deficiency indicator L with a predefined threshold TH and a step of deciding, on the basis of the result of the comparison, to take into account whether or not the heart rate signal (OUT) is taken into account. Method according to Claim 5, in which, during the decision step, the heart rate signal (OUT) is taken into account only if the deficiency indicator L is lower than the threshold TH. Method according to claim 5 or 6, in which the threshold TH is defined as follows:

where τ is a tolerance margin between 0 and 100 defining a maximum tolerated percentage of heart beats missed by the sensor (102) during the acquisition phase (T _acq ). Method according to claim 7, in which the margin τ is between 0 and 20. System comprising a heart rate sensor (102) and an electronic processing device (104), the electronic processing device (104) being configured to implement a method for estimating the quality of a heart rate signal ( OUT) provided by the sensor (102) according to any one of claims 1 to 8.